Reference should be made to the following articles: Japanese Patent Laid-Open Publication No. Sho 57-46986 (Patent Article 1); Japanese Patent Laid-Open Publication No. Sho 61-204188 (Patent Article 2); Japanese Patent Laid-Open Publication No. Sho 62-155282 (Patent Article 3).
Since the development of norfloxacin, considerable effort has been made worldwide to develop quinolone carboxylic acid-based antibacterial agents, which are also known as new quinolones and have now become important cures for infectious diseases.
The recent emergence of drug-resistant bacteria, such as Methicillin-Resistant Staphylococcus aureus (MRSA), Penicillin-Resistant Streptococcus pneumoniae (PRSP), and Vancomycin-Resistant Enterococcus (VRE), most of which are gram-positive bacteria, has posed a serious threat to the treatment of patients. Traditional quinolone carboxylic acid-based antibacterial agents have relatively weak antibacterial activities against gram-positive bacteria and thus are not considered as effective cures for the drug-resistant bacteria. Furthermore, the increasing incidence of Quinolone-Resistant Staphylococcus aureus (QRSA) makes the use of these drugs even more difficult.
While pyridobenzoxazine carboxylic acid-based antibacterial agents similar to the ones claimed in the present invention are described in, for example, Patent Articles 1, 2, and 3, none of these agents offer sufficient antibacterial activity against gram-positive bacteria, nor are they described to have antibacterial activity against drug-resistant bacteria such as those described above.